1. Field of the Invention
The present invention relates to a blood sampler and an adapter for use with the blood sampler.
2. Prior Art
For clinical examinations such as the test of serum or blood cells, blood samples are collected using a blood sampler typically constructed as follows.
The blood sampler comprises in general a tube holder for receiving an evacuated blood sample tube. A sampling needle penetrates a forward end of the tube holder so as to extend forwards, and an elastic sheath fits on a rearward end of the sampling needle so that its fine bore through the rearward end is openably closed. The blood sample tube, which must be evacuated corresponding to the needed quantity of blood sample, is composed of a closed-bottom cylinder and a penetrable plug plugged in the open end of the cylinder.
When the blood sample is to be taken, the sampling needle will be caused to pierce a vein, and then the evacuated tube will be forced into the tube holder so that the penetrable plug presses the elastic sheath in the direction of its axis. As a result, the rearward end of the sampling needle penetrates both the sheath and the plug whereby the needed quantity of blood sample is allowed to flow back into the tube in proportion to its degree of evacuation.
The inner diameter of the tube holders has been designed in general to match the outer diameter of the penetrable plugs plugged in the blood sample tubes. Since the latter diameter is almost the same for the various types of tubes, the conventional tube holders are also of almost the same inner diameter.
It is however a recent tendency that the blood sample tubes of a smaller diameter and thus closed with a smaller plug are preferred.
In a case wherein the conventional tube holder of a normal, or greater diameter is used with the recent smaller tubes, a comparatively large gap will appear between the holder and the tube. Such a large gap will render it difficult for the needle's rearward end to pierce a central portion of the plug. In other words, there is a fear that the needle will erroneously pierce the peripheral zone of the plug.
Generally, the peripheral zone is thicker than the central portion in the axial direction of the plug so that a stronger friction is provided between said zone and the wall of closed-bottom cylinder and the needle can easily pierce the thinner central portion.
If the needle pierces the thick peripheral zone of the plug against a strong resistance, then this resistance which may be stronger than the friction referred to above would cause an unintentional withdrawal of the plug from the cylinder, with the needle being pulled away from the plug.
It is also to be noted that automatic chemical analyzers are now employed widely, which are constructed such that the blood sample tubes are put on a rack and their unremoved plugs are pierced successively by a "testing" needle for sucking the blood samples out of the tubes.
For a speedy sampling of the tested blood samples, the blood sample tubes used with those analyzers must have the plugs less resistant to the testing needle which pierces them.
However, with such a blood sample tube, its elastic sheath compressed by the plug tends to repel the plug when the tube is set in the holder before sampling the tested blood. This repelling force is likely to exceed the plug's friction holding the needle. Thus, the blood sample tube will be pushed backwards so that the "sampling" needle is withdrawn from the plug. This phenomenon is called the "kickback" of the tube, and is a serious problem which must be resolved.